Slash bankers' bonuses, build more affordable homes, enshrine equal rights for agency workers and support better childcare provision. And while you're at it, stop top earners getting tax relief on pensions, axe the £16bn Trident missile programme, scrap ID cards and use the money to rebuild Britain's manufacturing base and protect key public services and jobs from cuts.

If Gordon Brown didn't know already, he was left in no doubt what Britain's most powerful union barons wanted from Labour when 15 general secretaries attended a four-hour lunch at Chequers with the prime minister on Friday.

And as the TUC conference begins today, perhaps for the first time in Labour's 12-year administration, the unions hold the whip hand. Labour's disastrous finances – earlier this year it was days away from financial meltdown – required big cheques from the unions to keep the party afloat. And with business shunning Labour and stuffing their cash into Conservative coffers ahead of an election expected in eight months, the government's campaign will be funded overwhelmingly by the likes of Unite, the GMB and Unison despite varying threats of withholding money.

"The situation over finances means everyone is sticking close to them," said a Labour insider. "Because of the tight situation, these people are important."

Also playing straight into union barons' hands is the bank crisis. Union leaders spent the last decade urging Labour to wean itself off the economy's over-reliance on the City. A plea ignored when Brown as chancellor gleefully hoovered up tax revenues from banks to pay for increased public spending.

GMB union leader Paul Kenny said: "One reason we have got in this shit is that the government was not using regulatory control. Now I would suggest that after the banking crisis it's time to deal with city barons. It's time to listen. If we learnt anything from the last two years it's clear that you can't trust the market to operate in our best interests. Our primary job is to look after the interests of our members."

"Tantalisingly there is a sense of Cool Britannia returning with the stock market and house prices going up," said the Labour insider. "The unions won't let them get away with that. When the banks were collapsing, ministers were talking about how we need to rely on the City less and build up our manufacturing base. They will want to see meat on those bones."

So what else do unions want? Speaking on the eve of its annual conference, TUC general secretary Brendan Barber said: "The key issue is getting much clearer. While we are still in recession there is no case for reducing spending. Don't get preoccupied with the deficit. That's one dividing line with the Tories. I have big fears in particular about public expenditure cuts they seem to envisage making. I profoundly think they're on the wrong side of economic history."

Barber is pressing Brown to resist cuts on essential services in favour of clamping down on tax loopholes deployed by the super-rich and corporations. The TUC leader wants Labour to ensure the tax burden on lower and middle-income workers eases, stating these groups have suffered under a Labour government. Wages as a proportion of GDP have actually fallen under Labour, Barber says.

"It makes no sense to hammer pay and conditions in the public sector," he said. "One of the strong messages is that we need to see better wages. What the economy needs to see is more demand."

Barber believes workers have done their bit to help the UK through the recession by taking pay cuts, pay freezes and accepting shorter working weeks. But that burden must now end.

Barber and union leaders like Tony Woodley of Unite and Unison's Dave Prentis are jointly demanding commitments from Brown that any cuts in spending will not hurt public-sector jobs and services. They are urging Labour to support public sector final-salary pensions unequivocally. It is thought a Conservative administration would axe them. Unions say scrapping final salaries would not generate savings now.

Building union Ucatt says its priorities are measures to force the insurance industry to pay £1.4bn in compensation for workers affected by pleural plaque, a heavy scarring of the lungs caused by exposure to asbestos. It is a move the insurance industry has resisted. Ucatt is also demanding that directors be legally forced to ensure good health and safety management and that gang-master licensing is extended to the construction industry.

Unions were delighted that business secretary Lord Mandelson canned the partial sale of the Royal Mail. They were also heartened by Mandelson's intervention in Jaguar. But the government's £1.5bn Future Job Fund, which has created 150,000 new jobs, "took a long time to deliver" according to Barber and needs extending.

Unions say they hold insights into Labour's heartlands – working class voters who have drifted away from the party in growing numbers in each successive election. A poll by the GMB of its members in every constituency said that the most important issues for their members were childcare and crime.

To many, a commitment by Labour to hold a referendum on proportional representation is just about the only policy that would inspire middle-class floating voters. It is a policy that now finds favour among the union leaders who for the first time in 90 years will debate the issue at congress this week.

Mark Serwotka, the PCS general secretary who placed the motion, said: "For too long there has been a democratic deficit where the outcome of a general election is decided on the votes of people in a few key marginals."

But to get the traditional Labour voters onside, Labour will have to move closer to what the unions are arguing for. A well-placed Labour insider said: "We're massively shocked by what happened in the European and local elections. We knew we had to do more to shore up our heartlands but not to this extent."

But as the polls suggest a Conservative general election victory is a certainty, unions will have to deal with a party that looks as if it may attempt to unpick key tenets of European employment and social laws. Most union leaders are resigned to dealing with the Conservatives but say they represent too many people – 6.2m members – to be ignored.

But memories of how the Conservatives dubbed unions "the enemy within" still scar union leaders. It's why they will still fund Labour's campaign and pray, however unlikely, for a miracle.